rusting

Heyo, So I bought a 2005 mustang gt a few months back, and I recently noticed a large amount of rust bubbles on the bottom of both rear quarter panels. :( I'm not sure I want to know this, but how much will it cost me approximately to fix? It a patch on both sides that is about 2x6 inches large...

Alright so recently there has been a squeak coming from my engine. Its a pretty constant squeak unless I'm under 1,200 rpm's. So I took it to a mechanic and he told me it was because my pulleys were rusting because my hood scoop was letting in water. Has anyone heard of your pulleys rusting...